With the rapid development of social economy, driving the rapid growth of the automobile industry, automobiles and other motor vehicles become one of the essential means of transportation in the current society. However, in order to gain more economic benefits, some semi-trailer users modify the vehicle size to increase the vehicle volume, so as to increase the one-time transportation volume of a vehicle and reduce the transportation cost, but this move is a serious violation of the safety standard for vehicle use. There are countless traffic accidents due to a vehicle overload every year, among which, semi-trailer accidents cause the most severe economic loss. Therefore, to guarantee the safety of vehicles, the vehicles must be inspected annularly according to the concept of a pin axle base, “a horizontal distance between a central axis of a traction pin of a semi-trailer and a horizontal geometric centerline of a non-turning axle group”, in the national standard GB1589-2016 published on Jul. 27, 2016, and pin axle base-related checking and inspection work requirements are raised. To detect the pin axle base, the position of the traction pin is required to be measured at first, but at the present, the traction pin of the semi-trailer is often detected by a manual measurement mode which is extremely low in efficiency, high in labor cost and easily restrained by a measurement tool during inspection of large-sized semi-trailers, and the measurement accuracy and the violation operation are hard to control.
As the measurement of the traction pin is more difficult than that of a length, a width and a height of a vehicle, it is imperative to develop a device for measuring the traction pin of the semi-trailer according to the new requirements of the country for vehicle inspection.